Electrical measuring systems

ABSTRACT

A system for measuring electrical power and including a pair of converters for providing a pair of output pulse trains, the duration of the pulse being proportional to the means squared value of input signals to the converters. A circuit is included for generating a signal proportional to the difference between corresponding pulses; where the input signals to the converters are E+I cos theta and E-I cos theta , the difference signal is essentially E I cos theta , the power sought.

United States Patent [72] Inventor [54] ELECTRICAL MEASURING SYSTEMS OTHER REFERENCES IBM Technical Disclosure Bulletin Vol. I 1, No. 1 l 4-1969,

Primary Examiner-John S. Heyman 9 Claims, 12 Drawing Figs. Attorney-Schiller & Pandiscio [52] US. Cl 328/144, v I

328/14] ABSTRACT: A system for measuring electrical power and in- [g1] lntiCl G06g 7/20 eluding a pair of converters for providing a pair of Output 0] Fle dofseal'ch 328/141, pulse trains the duration of the Pulse being proportional to I 144 the means squared value of input signals to the converters. A circuit is included for generating a signal proportional to the [56] References cued difference between corresponding pulses; where the input UNITED STATES PATENTS signals to the converters are E+1 cost? and E-I cos0 the dif- 3,458,823 7/ 1969 Nordahl 328/141 X ference signal is essentially E I c050, the power sought. 3,484,593 12/1969 Schmoock et al. 328/144 X I E- DEMODULATOR v-c S COMPARATOR AMPLIFIER AND DELAY FILTER GENERATOR 24 i FREQUENCY f GENERATOR SHAPER DC REFERENCE PATENTEDJANMHYZ 3.633116 SHEET 1 BF 3 22 26 28 30 E In DEMODULATOR v-c g COMPARATOR AMPLIFIER AND DELAY FILTER GENERATOR 24 f FREQUENCY F32 GENERATOR SHAPER 1 /6. I DC REFERENCE 46 47 49 50 [T30 Z SYNCHRONOUS VOLTAGE 38 DEIvIODuLATOR CONTROLLED I 43 DELAY GENERATOR 64 34 DC REFERENCE 54 32 SHAPER 62 2MH 7- H05 CLOCT I52 66 72 vOLTAGE 30 Dc CONTROLLED 38 AMPLIFIER DELAY W 69 GENERATOR SHAPER 7O 67 T r 4 DC REFERENCE T] I T1 F/G. 2.

c i n FL PETE/P L. R/CHMA/V //Vl/E//T0/?. D IL FT I I I BY pand ATTORNEYS PAIEIIIEIIIIII 4m 3.333.116

SHEET 2 BF 3 AMPLI IER DEMODULATOR CONVERTER "1 T r 3.2 DC W60 SHAPER REFERENCE CLOCK -52 22 E 76 42 r p80 f VOLTAGE 30 DC ZSB DIFFERENCE CONTROLLED AMPLIFIER STORE AMPLIFIER DELAY 34 GENERATOR 38 32\ SHAPER REFERENCE 60 9/ 84 86 HI? A/D D/A I CONVERTER CONVERTER I 59 MLA -JHW O FIG 7 92 88 1 CONVERTER r708 rim :SUBTRACT MEASURE F/& 9 I06 E2 CONVERTER l--T i Fn +l F1 F1 I 'L l--T -i B i 2]: Fl I I .L- T] C j l I F1 I- z PETE/F L, R/CHMA/V F/G 70 //Vl E/V7'0/?.

ATTORNEYS.

1 ELECTRICAL MEASURING SYSTEMS This application relates to measurement of electrical signals and more particularly to the conversion of the mean squared value of an input signal into a time function which can be readily digitized, and use ofsuch conversion to provide a multiplier.

Perhaps the most apparent use of a system which converts a mean squared value of a signal into digital form is to measure electrical power in an AC circuit in accordance with the quarter square principle. The latterrecognizes that if an input voltage'is E and the input current is I cos (both E and I being variable in time), the power P can be represented as:

l. P=(E+I cos'OV-(E-I cos 0) because equation (I) simplifies to 2. PIK=EI cos 0 where K=4.

In the prior art, most power measurements have been made by applying the unknown current and voltage to the coils of a moving-coil wattmeter, or to the inputs of dynamometers of various types. Such systems are very limited in response speed, frequency range and accuracy; they tend to be clumsy to use and are suitable primarily under laboratory conditions if one seeks to obtain any reasonable degree of accuracy.

A principal object of the present invention is therefore to provide means for measuring the power in a system with high accuracy and in very short times, typically to several MHz and in the order of a'few hundredths of a percent accuracy to 50 kHz. and within a few seconds. Another object of the present invention is to provide such a power measuring mea'hs which provides the computed power in digital readout from. Yet another object of the present invention is to provide such a power measuring means which requires substantially no adjustments by an operator save perhaps setting up range switches.

The basic system employed is an implementation of the quarter-square method above described. Therefore, yet another principal object ofthepres'ent invention is to provide means for squaring a signal'ati'lplitude, on a wideband basis. Yet another object of the present invention is to provide such a squaring means which provides the computed value of the square in digital form. In a more general sense in some aspects, yet somewhatmore'lirhited sense in other, an object of the present invention is' toprovide'means for generating a power function of the type A where A is the amplitude of an input signal.

If one notes that'the ultimate result sought as expressed in equation (2) is a product, it will be apparent that, generally, a principal'object of the present invention is to provide a multiplier.

These foregoing and other objects of the invention are effected by using a'closed loop system for converting the amplitude of an input signal intoan output signal having a temporal parameter proportional "to the square of that amplitude.

To achieve the foregoing and other objects, the present invention generally contemplates the provision of a power-totime conversion device which accepts an input signal and generates a output signal having a temporal parameter proportional to the square of the amplitudeof the input signal. Basically, this device comprises a comparator for comparing the power in the input signal with the power in a feedback signal, and means for generating an iterative signal having a time parameter, such as period or frequency proportional to the difference or error signal yielded by the comparator. The iterative signal is employed to generate the feedback signal such that the only'variable in the latter is the time parameter. The multiplier thus comprises two such power conversion devices, the inputs of which are intended respectively to have applied thereto signalscorresponding to the sum of and the difference between multiplier and multiplicand values. The outputs of the conversion devices are then respectively coupled to means for subtracting the time parameter of the output signal of one device from the time parameter of the output signal of the other device. The difference in temporal parameters thus obtained in converted in appropriate means iiito an output signal for recording or display.

The foregoing and other objects of the present invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the apparatus possessing the construction, combination of elements, and arrangement of parts, all of which are exemplified in .the following detailed disclosure, and the scope of the applications of which will be indicated in the claims.

For a fuller understanding of the'nature and objects of the present invention, reference should be made to the following detailed description taken in connection with the accompanying drawings wherein FIG. 1 is a block diagram of a generator of an output signal having a temporal parameter proportional to the square of an input signal;

FIG. 2 is a group of exemplary waveforms illustrative of the operation of the generator of FIG. 1;

FIG. 3 is a more detailed diagram, partly in block form, showing one embodiment of the generator of FIG; 1.

FIG. 4 is a diagram, partly in block, of yet another embodiment of the generator of FIG. 1.

FIG. 5 is a diagram, partly in block form of a generator of an output signal having a frequency proportional to the square of an input signal;

FIG. 6 is a diagram, partly in block form, of yet another device for providing pulsed output signal having a pulse duration proportional to the square of an input signal;

FIG. 7 is a block diagram of atypical track-and-store circuit useful in the embodiment of FIG. 6;

FIG. 8 is another version of a'track-and-sto re circuit useful in the device of FIG. 6;

FIG. 9 is a block diagram illustrating the multiplier of the present invention;

FIG. 10 is a group of waveforms illustrating the operation of a typical embodiment of the device of FIG. 9; 7

FIG. 11 is a block diagram of'a more specific implementation of the device of FIG. 9; and

FIG. 12 is a circuit diagram, partly in block form illustrating a device for obtaining sum and difference values for use as input signals to a system such as themultiplier of FIG. 9

Referring now to the drawings, particularly in FIG. 1, there is shown a basic embodiment of one'converter of the present invention. The circuit includes power comparator 20 shown as a generalized device which includes a pair of input comparison terminals 22 and 24 and which supplies an output signal either AC or DC proportional'to the'difference between the values of the electrical power of the signals applied at input terminals 22 and 24. Input terminal 22 is intended to have applied thereto an input signal E, and terminal 24 is connected so that a feedback signal E, can be applied thereto.

Thus, the power comparator neednot measure electrical power accurately, it need only furnish 'zeroch'arige in output for zero difference in the powers, of thetwo'applied signals, E and E,, and some finite, not-necessarily-linearly-related output for a difference between the power in E and E, that is nonzero.

The output of the comparator is connected to amplifier 26 and thence to demodulator-filter 28 in the case where the comparators output is AC. When the comparators output is a DC representing the error or difference betweenthe electrical powers of the two input signals, demodulator-filter 28 is, of course, unnecessary.

The output of demodulator-filter 28 (or directly from the amplifier when the output from the power comparator is a'DC signal) is connected to voltage controlled delaygenerator 30. In its simplest form, the latter is a multivibra'tor whose delay is determined, roughly, by the magnitude of the DC potential applied. The design of such a multivibrato'r is well known to those skilled in the art. Delay generator 30 is preferably clocked; i.e., it generates repetitive pulses, the pulse widths of which are DC controlled, at a repetition'rate determined by precision frequency generator 36. The frequency typically can be 20 Hz., for example, and the pulse width might vary from 0 to some reasonable fraction of a whole cycle, such as one-half (25 milliseconds) or three-quarters (37.5'milliseconds) corresponding with zero and full scale input power respectively.

Output of voltage-controlled delay generator 30 is applied to shaper 32, which is also furnished with a DC reference on terminal 34. The shaper provides at its output a signal of precision peak amplitude established by the DC reference and over a time interval determined by the pulse width of the concurrent pulse from the delay generator. The period of each pulse cycle from the shaper is, of course, the same as the period of the pulse from the delay generator, and, in turn, equal to the period of the output from frequency generator 36. It will be understood that the value of the DC reference is fixed; that is, remains relatively invariant during at least one cycle of the comparator or is short-term invariant. However, the DC reference value should be adjustable over long term thereby providing flexibility in operating and indeed may even be automatically adjustable in terms of the amplitude of the input similar to a conventional automatic range changing system.

The shaper output is furnished as the second input at terminal 24 to power comparator 20 to close the feedback loop. The output of generator 30 applied to terminal 38 is a pulse whose duration is accurately proportional to the square of the r.m.s. value of the input E or (E,,, It is quite independent of the accuracy of generator 30and depends only on the accuracy of the DC reference voltage applied at terminal 34, the ability of the power comparator to function as an effective null-device for equal power inputs, and the gain of amplifier 26.

That the duration of the width of each of the periodic output pulses applied to terminal 39 is proportional to (E,,, (my may be seen from the following considerations. W reference to FIG. 2, the input applied to terminal 22 in FIG. 1 is shown as waveform A for exemplary purposes. It need not be regular, undistorted, or even periodic for that matter for the device of FIG. 1 to work properly. FIG. 2B shows the output from the power comparator in thecase in which the electrical power in each of the two signals E and E, have not yet nulled, so that there is a small residual error at the comparator output, which is assumed to be variable DC for exemplary purposes. FIG. 2C shows an exemplary output from delay generator 30, a wave of fixed period T and variable duty cycle, the positive portion of which has variable duration FIG. 2D shows the waveform of FIG. 2C after shaping; i.e., with a flat-topped, fixed amplitude value. It should be noted that typically the period of the comparator output (FIG. 23) will be at least to 20 times longer than the longest periods of the input and feedback waves (FIGS. 2A and 2D) in order that the thermal power comparator can at least partially stabilize during each half cycle of FIG. 2B.

The electrical power supplied to an arbitrary selected 1- ohm resistor by the signal of FIG. 2D, assuming its amplitude IS e,

The upper limit may be set at 1 in view of the fact that the wave of FIG. 2D is zero for all times except from 0 to 1.

Equation (3) may be reduced by straightforward integration to P=( l/T )e r Thus, the power in the feedback signal is proportional to the fixed constants e (the reference voltage applied to terminal 34) and T the fixed period of the periodic output from generator 30 as set by the frequency standard of generator 36. It is also proportional, directly and linearly, to the duration 7 of the positive portion of the wave from shaper 32. Thus, a measurement of the duration 1', by conventional meanssuch as by counting the number of pulses of a precision pulse generator that fall within the durationwill yield a highly accurate number for the electrical power applied in the signal E,,,, which is itself proportional to (E,,, Thus, the entire converter of FIG. 1 is referred to as a V/S or volts-to-square converter, since a temporal parameter of its output (time interval per cycle) is linearly proportional to the square of the r.m.s. value of its input.

With reference now to FIG. 3, there is shown a more specific version of the device of FIG. 1 wherein like numerals denote like parts. The power comparator 20 comprises an electromechanically, periodically operated switch 40 driving an indirectly heated thermocouple 42. When the armature of switch 40 contacts the upper contact as shown, it connects thermocouple 42 to the input signal E applied to terminal 22. When the switch armature contacts the lower contact, it connects the thermocouple input to terminal 24 and so to the source of feedback signal E,, shaper 32. Thus, the thermocouple is alternately heated with the input and the feedback signal so that its output potential moves between two levels, one dependent upon the power generated by the input E applied to the fixed thermocouple input resistance,, or in effect dependent upon the square of the r.m.s. value of E and the other dependent upon the square of the r.m.s. value of E,as required by the basic scheme of FIG. I.

Amplifier 26 and demodulator-and-filter 28 of FIG. 1 are shown in more detail in FIG. 3, as AC amplifier 44, coupling capacitor 46, synchronous demodulator 47 and an integrator (filter) composed of operation amplifier 48, withinput resistor 49 and feedback capacitor 50. Voltage controlled delay generator is designated 30.

A high-frequency clock 52, a source of timing pulses at a repetition rate of, for example, 2 MHZ is required to operate and control the various counting and timing operations in a practical power measurement. Its output is divided by 10 in five-decade counter 53.

The selection of the clock frequency at 2 MHZ is arbitrary. It could be much higher, thereby, however, implying more complexity in the associated counting equipment. Alternatively, it could be much lower, thereby implying less resolution in the final measurement. The figure of 2 MHz provides a resolution of better than one part in 10,000 (or 0.01 percent) even at one-tenth of full output; and provides 0.00l percent resolution at or near full output, as will be seen.

The output from the five-decade counter is applied over line 54 to delay generator 30 to initiate the pulses from the latter and control the repetition rate or period of the pulse train from generator 30. The pulse train on line 54 is at a 20 Hz. rate for the example ofa 2 MHz clock and a l0 divider.

There is provided a second divider 56, selected to divide further the output frequency from divider 53 by a factor chosen for exemplary purposes as 20. The output of this divide-by-ZO counter 56 is, therefore, one Hz. and is suitable for actuating the armature of switch 40 to alternately sample the two signals, E, and E,as earlier described. Thus, line 57 from the output of divider 56 is connected to actuate relay coil 58, the contacts shown in switch 40 being contacts of the relay. Another system for accomplishing switching would be to use electronic components such as field-effect transistors to connect and disconnect E, and E, alternately to the input of the heater of the indirectly heated thermocouple 42, or to an amplifier driving the heater.

Output from the divider 56 is also connected to provide the reference or demodulating signal for the synchronous demodulator 47 as shown.

The DC reference source input 34 of shaper 32 is shown supplied from an explicit fixed DC reference source 60. This latter will typically take the form of a precision reference zener diode with appropriate preregulation. For highest accuracy and stability, reference source 60 will ordinarily be housed within a precision component oven and maintained thereby at constant temperature. However, as previously noted, the term fixed here does not exclude adjustability over the long term and is to be considered as meaning invariant only over short term.

The output from the same 2 MHz clock 52 that initiates all of the other timing operations is gated via AND-gate 62 by the output of the generator 30, to provide at terminal 64 a train of pulses which is proportional in number to (E (mu) as may be required if the square alone is what is desired. The gate signal from the output of generator 30 is also applied to output terminal 38.

Referring now to FIG. 4, there will be seen another implementation of an E /Time-lnterval converter, in which the comparison between (E,,,) and (E,) is carried out continuously, instead of on a switched or intermittent basis as in the device of FIG. 3, although like numerals denote like parts. The embodiment of FIG. 4 thus has the advantage of somewhat higher speed that theloop of FIG. 3, but suffers somewhat in accuracy. In cases in which lower accuracy is needed but speed is paramount, the implementation of FIG. 4 should be employed.

In FIG. 4, the input E is applied directly and nonintermittently to heater 65 of 'an indirectly heated thermocouple 66, while the feedback voltage E, is also nonintermittently applied to heater 67 of second indirectly heated thermocouple 68. The two thermocouple outputs, appearing on thermocouple elements 69 and 70, respectively, are summed series opposing as shown, so that if the power inputs to the two thermocouples are equal, the output at the high end of thermocouple element 69 applied to DC amplifier 72 will be zero.

Since the error from the output of the series-opposing sum of thermocouple element outputs applied to the DC amplifier is a DC potential, the output from the DC amplifier may be directly applied to generator as shown. The output of the latter is again shaped by shaper 32, driven also by DC reference applied to terminal 34, the shaper output being of the same pulse width as the output from generator 30, but with an amplitude precisely equal to the DC reference. Shaper output is E,, and is applied to the heater 67 of thermocouple 68 as described.

The other aspects similar to FIG. 3 are omitted from FIG. 4 for simplicity. FIG. 4 merely serves to shown a difference in implementation for the EfTime Interval converter of FIG. 3, and makes no attempt to duplicate the other features remainder ofFIG. 3.

The device shown in FIG. 5 is another squarer or generator of an iterative output signal having a temporal parameter proportional to the square of the amplitude of an input signal; the temporal parameter in this instance is the frequency of the output signal. This device is useful in forming a multiplier as will be described hereinafter, but being known in the art will only be described briefly here. It can be structured in a manner quite similar toFIGS. l and 3 like numerals denoting like parts, but includes voltage-to-rate converter 74 in place of the converter 30 of FIG. 1. Obviously, converter 74 can be a well-known voltage controlled oscillator which provides a pulse train with fixed duration pulses at a frequency approximately proportional to the input DC.

The volts/rate converter requires no trigger from a 20 Hz. clock; so none is provided; however, since a low-frequency signal is still needed to actuate the input switch and simultaneously to gate the synchronous demodulator 47, it is provided for simplicity in FIG. 5 by an asynchronous or freerunning, 1 Hz. clock 52. Output from the volts/rate converter applied to terminal 38 constitutes the output from the entire system.

The device of the type shown in FIGS. 1 and 3 and 4 are preferred over that of FIG. 5 for use in forming a multiplier for a variety of reasons, not the least of which are that one can control with much greater accuracy and over a much larger range, pulse width or duration than pulse train repetition rate or frequency. Further, considerably less bandwidth requirements are imposed upon the elements of a system when the frequency is fixed as in the devices generating variable pulse width trains.

FIG. 6 shows still another different implementation of the basic generator of an output signal having a temporal parameter proportional to the square of an input signal very closely allied to the device of FIG. 1. FIG. 6 shows a different way of using the equal-power, time-interval scheme to obtain a timeinterval that is proportional to the square of the input voltage, and comprises input terminal 22 connectable through switch 76 to the heater of thermocouple 42. The output of thermocouple 42 is connected to the input of of DC amplifier 78 and the latter, in turn, is connected at its output to the input of switchable track-and-store circuit 80. The output of amplifier 78 and the output of circuit are respectively connected to corresponding input terminals of difference amplifier 82. The output of the latter is connected to control voltage-controlled delay generator 30 of the type hereinbefore described. The output of the latter is connected to both output terminal 38 and an input of shaper 32. The latter is, as previously noted, connected also to DC reference source 60 which provides a precision amplitude value for the pulses from the output of the shaper. The latter output is connectable alternatively through switch 76 to the thermocouple heater.

The input switch 76 is now not synchronously and periodically alternated from one contact to another, to obtain a continuous, carrier-operated comparison of input power with feedback power. Instead, the input switch rests in the upper position connected to terminal 22 for a period of 5 to 10 seconds, until the input thermocouple settles to a fixed value proportional to the square of the input voltage E,,,. The thermocouple output is amplified by DC amplifier 78 and is stored either in an analog sense or else digitally in track-and-store device 80. Then the switch 76 is switched to the lower or feedback contact, connecting to the shaper output. The DC ampliagain amplifies the thermocouple output, but synchronously with switch 76, the track-and-store device 80 has been switched into the store mode, so that the difference amplifier 82 receives simultaneously a DC signal from the track-and-store device 80 representing the output of the thermocouple 42 with E, applied, as well as the present DC signal from the DC amplifier with the feedback voltage applied to the input thermocouple.

The difference amplifier amplifies any difference between these two potentials, and provides an error or difference signal which controls the pulse width generated by generated 30. The output of the latter drives shaper 34 to generate the required feedback pulses. When the loop has nulled this time, the output at terminal 38 will be the stored pulse width as required, proportional to the (E,-,, as required. In this system, an entire new determinationof the value is obtained only every 5 or 10 seconds, as opposed to the previous systems in which it is continuously available.

FIG. 7 shows a typical digital form of a track-and-store device that can be employed for circuit 80 in FIG. 6. It is merely an A/D (analog-to-digital) converter 84 followed by a D/A (digital-to-analog) converter 86. When the register or counter within A/D 84 is disconnected from its inputs, it is effectively put into the store mode and will store the digits indefinitely. With the register or counter in A/D converter connected, D/A converter 86 will provide a DC output proportional to the digits as required to track the input to converter 84. FIG. 8 shows an analog track-and-store device formed of an integrator comprising a high gain inverting amplifier 88 with an input resistor 89, feedback resistor and feedback capacitor 91. A switch 92 between the input of amplifier 88 and the junction of resistors 89 and 90 is opened to initiate storage thereby disconnecting any further current flow into the input of the amplifier and providing a constant, stored analog potential at the output terminal 313. When switch 92 is closed, the output of the system tracks the input.

To form a multiplier according to the present invention two V/X converters and 102 are employed as shown in FIG. 9, respectively, having input terminals 104 and 106 at which input signals such as E and E can be applied. The outputs of converters 100 and 102 are connected to the input of subtraction circuit 108. The output of the latter in turn is connected to an output circuit 110 for measuring, display, or the like.

The operation of the block diagram of FIG. 9 is advantageously described in connection with the waveforms of FIG. 10. For simplicity, one can assume that converters 100 and 102 are of the type shown in FIG. 3 and both operate from a common DC reference and a common clock so that they are synchronous. Thus, exemplary output signals from converters 100 and 102 graphed on a common time base are shown graphically in FIGS. 10A and 10B, respectively. The leading edges of the pulses are simultaneous and their periods T are identical because of the common clock, their amplitudes are identical because of the common DC reference, and they differ only in pulse width 1, and 1 By subtracting in circuit 108 the pulse widths of corresponding pulses in one train from the other, one obtains a series of difference (ff-T pulses shown in FIG. 10C. Typically, circuit 108 can be a multivibrator triggered respectively on" and ofF by successive negative-gain pulse transitions or the like. Circuit 110 to which the difference pulses are applied may be a conventional counter in its so-called period mode of operation. The output of the counter will be a digital display of the difference 7 -7 which will be accurately proportional to the difference between the mean squares of E and E, as described.

If the inputs E and E are (A-l-B) and (A-B), respectively, then the counter will read the product AB/K where K=4 as previously described. The invention in effect then is a multiplier: a primary purpose of the multiplier is to accurately determine power.

If E and E are (E+I cos and (E-I cos 6), then the digital number displayed on the counter will be proportional to the power presented by the product El cos 0. Appropriate scaling may be introduced by selecting the frequency of the highfrequency pulses counted during the difference period in the counter, by selecting the number of periods over which the measurement will be averaged in the counter, and by selecting the maximum duration of r, and 7' Referring now to FIG. 11, there is shown a detailed version of the power-measuring implementation of FIG. 9, using the specific E /Time Interval converter of either FIG. 3 or of FIG. 4. As in FIG. 9, two E /Time Interval converters 112 and 114 are employed, for respective inputs E, and E Common DC reference source 116 supplies DC to the shapers within each of the E /Time Interval converters. A common clock, 118, chosen to provide signals at a typical frequency of 2 MHz, drives a common l0 divider 120 the output of which feeds a common divide-by-20 counter 122. The outputs of dividers 120 and 122 are connected to both of the EfTime Interval converters in a manner previously described in connection with FIG. 3.

The outputs of converters 112 and 114 are as shown in FIGS. A and 108, respectively, and as already described in connection with FIG. 9. Time-interval subtraction is shown explicitly in FIG. 11 (instead of just in block form of subtraction circuit 108 in FIG. 9), as the inversion by inverter 116 of the output signal of converter 114 and the application of this inverted signal to either with the noninverted output signal from converter 112, to AND-gate 118. Output of AND-gate 118 is as shown in FIG. 10C: a signal whose duration is equal to the difference in durations between an output pulse from converter 112 and that from converter 114. This signal from gate 118 subsequently gates the 2 MHz clock pulses in another gate 120 at the start of the time-interval measurement. Output from gate 120 is counted by counter 122, with appropriate start pulses derived from the output of the 10 divider 120. Buffer store 124, activated by the trailing edge of the pulses from divider 120 via inverter 126, transfers the count into a register to furnish nonfiickerin g display unit 128 (for example, an array of Nixie tubes) in conventional manner well known to those skilled in the art.

It will be appreciated that the circuit of FIG. 9 can also be implemented using the converter shown in FIG. 5. In such instances, the subtraction circuit 108 would need to provide a signal representing the difference between the frequencies or repetition rate of the two signals thereto, and could comprise an appropriate version of the well-known beat-frequency oscillator or an updown converter for example. The measuring circuit 110 would then merely need be a frequency meter to indicate the value of the difference signal, or a digital display for the output of the counter, as the case may be.

Lastly, in order that the multipliers of FIGS. 9 and 11 be an AC power measuring system, as earlier noted, E and E would each be selected as one of the two summations (E-l-I cos 0) and (E-I cos 0), where E and I are respectively the values of potential and current in a circuit, and cos 0 is the power factor. An exemplary circuit useful for providing these input signals to terminals 104 and 106 of FIG. 9, for example, is shown in FIG. 12.

In FIG. 12, there is shown in block a power-consuming system 130, the AC power input to which one wishes to measure. The leads 131 and 132, respectively, provide the AC power to the system. A voltage sensor or primary coil 134 is connected across leads 131 and 132, and inductively coupled to secondary coil 136 to form a transformer. A current sensor or coil 138 is inductively coupled to lead 132. One end of coil 138 is grounded, the other being connected through input resistor 144 to a second summing junction 146. Coil is shunted by resistor 139 to limit voltage. Similarly, one end of the coil 136 is grounded, the other being connected through input resistor 148 to junction 142. The latter is connected to the input of very high gain, inverting amplifier 150 which has a feedback resistor 152 connected between output terminal 154 and summing junction 142. Terminal 154, in turn, is connected through another input resistor 156 to summing junction 146. The latter is connected to the input of very high gain inverting amplifier 158 which has a feedback resistor 160 connected between its output terminal 162 and junction 146. The ohmic values of resistors 148, 140, 152, 156, and 160 are all preferably the same, but resistor 144 is one-half the value of resistor 156.

In operating, it will be appreciated that the voltage across coil 136 is proportional to the input voltage E to system 130, and the voltage across coil 138 is proportional to I cos 0. In as much as amplifier 150, and its feedback and input resistors is simply a summing operational amplifier, the output from the latter, apparent at terminal 154, is proportion to the inverted sum of the inputs or E+I cos 0). The inputs, however, to amplifier 413, through resistors 156 and 144, are respectively proportional to (E+I cos 0) and 2 I cos 0 because of the 2:I ratio of values of these resistors. Amplifier 413 and its associated resistors constitute another summer which provides an output proportional to the inverted sum of its inputs or (EI cos 0). Thus, the sum and difference signals are obtained and their polarities can, of course, easily be inverted if desired, although the power inherent in the signals is independent of sign which merely indicates relative phase.

Since certain changes may be made in the above apparatus without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted in an illustration and not in a limiting sense.

What is claimed is:

1. A device for generating an output signal having a temporal parameter proportional to the mean squared value of an input signal, and comprising in combination means for producing an iterative signal which is a train, at a fixed repetition rate, of substantially flat-topped waves of fixed amplitude and variable duration,

means for comparing the mean squared value of said iterative signal with the mean squared value of said input signal so as to derive a difference signal;

said means for producing said iterative signal being responsive to a control signal proportional to said difference signal so that as said difference signal tends toward zero, said duration varies such that said mean squared value of said iterative signal tends toward a preselected ratio with the mean squared value of said input signal.

2. A device as defined in claim 1 wherein said ratio is unity.

3. A device as defined in claim 1 wherein said means for comparing comprises first and second terminals at which respectively said input signal and said iterative signal are intended to be applied, a thermocouple having an electrically actuated heater, and switching means for alternately connecting said first and second terminals to said heater.

4. A device as defined in claim 3 including means for generating a train of timing signals and means for periodically switching said switching means in accordance with said timing signals.

5. A device as defined in claim 4 including means for amplifying the output signal from said thermocouple;

demodulator means controlled by said timing signals for synchronously demodulating the output signal from said means for amplifying; and

means for filtering the output signal from said demodulator means to generate said control signal.

6. A device as defined in claim 1 wherein said means for producing said iterative signal comprises means for producing said flat-topped waves at a fixed repetition rate, and shaper means for fixing the amplitude of said waves.

7. A device as defined in claim 1 wherein said means for comparing comprises first and second thermocouples each having a separate electrically actuated heater, means for connecting one of said heaters to be actuated by said iterative signal and means for connecting the other end of said heaters to be actuated by said input signal.

8. A device as defined in claim 1 including means for filtering said difference signal to provide a substantially DC control signal;

said means for varying said temporal parameter being a multivibrator for producing substantially rectangular waves the duration of each of which is controlled in accordance with said control signal.

9, A device as defined in claim 3 including track-and-store means alternately operative for storing the output signal from said thermocouple or for providing an output signal which tracks the output signal from said thermocouple;

means for deriving said difference signal between alternate stored and tracked output signals from said thermocouple, and

means for synchronizing the alternate operation of said track-and-store means with the operation of said switching means. 

1. A device for generating an output signal having a temporal parameter proportional to the mean squared value of an input signal, and comprising in combination means for producing an iterative signal which is a train, at a fixed repetition rate, of substantially flat-topped waves of fixed amplitude and variable duration, means for comparing the mean squared value of said iterative signal with the mean squared value of said input signal so as to derive a difference signal; said means for producing said iterative signal being responsive to a control signal proportional to said difference signal so that as said difference signal tends toward zero, said duration varies such that said mean squared value of said iterative signal tends toward a preselected ratio with the mean squared value of said input signal.
 2. A device as defined in claim 1 wherein said ratio is unity.
 3. A device as defined in claim 1 wherein said means for comparing comprises first and second terminals at which respectively said input signal and said iterative Signal are intended to be applied, a thermocouple having an electrically actuated heater, and switching means for alternately connecting said first and second terminals to said heater.
 4. A device as defined in claim 3 including means for generating a train of timing signals and means for periodically switching said switching means in accordance with said timing signals.
 5. A device as defined in claim 4 including means for amplifying the output signal from said thermocouple; demodulator means controlled by said timing signals for synchronouzly demodulating the output signal from said means for amplifying; and means for filtering the output signal from said demodulator means to generate said control signal.
 6. A device as defined in claim 1 wherein said means for producing said iterative signal comprises means for producing said flat-topped waves at a fixed repetition rate, and shaper means for fixing the amplitude of said waves.
 7. A device as defined in claim 1 wherein said means for comparing comprises first and second thermocouples each having a separate electrically actuated heater, means for connecting one of said heaters to be actuated by said iterative signal and means for connecting the other end of said heaters to be actuated by said input signal.
 8. A device as defined in claim 1 including means for filtering said difference signal to provide a substantially DC control signal; Said means for varying said temporal parameter being a multivibrator for producing substantially rectangular waves the duration of each of which is controlled in accordance with said control signal.
 9. A device as defined in claim 3 including track-and-store means alternately operative for storing the output signal from said thermocouple or for providing an output signal which tracks the output signal from said thermocouple; means for deriving said difference signal between alternate stored and tracked output signals from said thermocouple, and means for synchronizing the alternate operation of said track-and-store means with the operation of said switching means. 